Problem Using Bipolar Transistor as a Switch

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Discussion Overview

The discussion revolves around using a bipolar transistor as a switch to convert a 5V signal from an infrared encoder to a 24V signal. Participants explore various approaches and considerations related to circuit design and component selection.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification
  • Experimental/applied

Main Points Raised

  • One participant expresses difficulty in using a bipolar transistor for switching from 5V to 24V and questions if they are missing something in their approach.
  • Another participant suggests that running the first stage off of 24V might be necessary, indicating that a 5V pull-up stage may not effectively control a 24V high-side switch.
  • A different participant proposes using an open-collector stage to convert the 5V signal to 24V if the first stage cannot operate at 24V.
  • Concerns are raised about potential damage to components if the first stage is run at 24V, and a participant mentions researching a specific product for voltage conversion but questions its response time.
  • Clarification is provided that the linked product is a DC-DC converter, and the focus should be on converting a 5V logic signal to a 24V logic signal using an open-collector BJT stage.
  • The original poster acknowledges their unfamiliarity with open-collector stages but expresses willingness to learn and implement the advice given.

Areas of Agreement / Disagreement

Participants present multiple approaches to the problem, with no consensus on the best method yet. Some suggest using an open-collector stage, while others highlight potential issues with component compatibility and circuit design.

Contextual Notes

There are unresolved concerns regarding the compatibility of the components and the specifics of the circuit design, including assumptions about voltage levels and the response time of suggested solutions.

Who May Find This Useful

Individuals working on electronics projects involving signal conversion, particularly those using bipolar transistors and open-collector configurations.

lindhaw
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Im new here and I am currently working on a small IR encoder project. I have the encoder working great but now I need to use the 5vdc signal that comes from the encoder and make it 24vdc. I am currently trying to use a bipolar transistor but its not working. The basic diagram that I am going off of is attached along with the schematic of the optical encoder schematic. Am i way off track or am I missing something obvious.

BTW I am using 20k for R1 and 200K for R2 for the switch
 

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lindhaw said:
Im new here and I am currently working on a small IR encoder project. I have the encoder working great but now I need to use the 5vdc signal that comes from the encoder and make it 24vdc. I am currently trying to use a bipolar transistor but its not working. The basic diagram that I am going off of is attached along with the schematic of the optical encoder schematic. Am i way off track or am I missing something obvious.

BTW I am using 20k for R1 and 200K for R2 for the switch

Welcome to the PF.

Can you run the first stage off of 24V? A 5V pullup stage will not shut off a 24V high-side switch stage...
 
If you can't run the first stage at 24V, use an open-collector stage to convert from 5V to 24V.
 
lindhaw said:
I don't think I can do that because I think it would just burn up the emitter and possibly the receiver. I've also been looking into this http://www.goldmine-elec-products.com/prodinfo.asp?number=G18694 but I've never used anything like that so I am not sure if the response time will be fast enough.

Your link is just a DC-DC converter to convert a 5V power supply to a 24V voltage source.

What you want is a way to convert a 5V logic signal to a 24V logic signal, correct?

The way to do that is with an open-collector BJT stage. Are you familiar with those yet?
 
Ya that's correct. I am not familiar with those yet. Is that something that I could make or is that something that I should just buy?
 
ok dumb question sorry I just looked it up and I think i can manage one of those. Thanks for the advice! Ill let you know how it goes!
 

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